1. Field of the Invention
The present invention relates to an electromagnetic pump, and more particularly to an electromagnetic pump having an exhaust-control valve by which the quantity and pressure of exhausted oil can be maintained constant by automatically controlling the pressurizing of the oil.
2. Prior Art
An electromagnetic pump is an appliance for supplying fluid, and is generally used for supplying oil to a burner in a boiler system.
FIG. 7 is a hydraulic circuit diagram of a conventional electromagnetic pump 10. As shown in FIG. 7, electromagnetic pump 10 has a suction section 20 for introducing oil from an oil tank 12, a development section 30 for increasing the pressure of the introduced oil, and an exhaust section 40 for exhausting the oil pressurized through development section 30.
Suction section 20 includes a suction nozzle 22 interconnected to oil tank 12 so as to receive oil therefrom, and a suction filter 24 interconnected through a first oil path 61 to suction nozzle 22.
Development section 30 includes a suction check valve 32 interconnected to suction filter 24 so as to receive oil therefrom, an exhaust check valve 34 interconnected through a second oil path 62 to suction check valve 32, and an actuating section 31 for pressurizing the oil having been introduced through suction check valve 32 and exhausting the pressurized oil through exhaust check valve 34.
Exhaust section 40 includes an exhaust valve 44 for intermittently exhausting oil having been introduced through a fifth oil path 65 from development section 30 into a burner (not shown), an exhaust nozzle 48 for guiding the pressurized oil having passed exhaust valve 44 into the burner, and a relief valve 42 for controlling the pressure of the exhausted oil. One end of relief valve 42 is interconnected to a sixth oil path 66 branched out from fifth oil path 65, while the other end of relief valve 42 is connected to a seventh oil path 67 branched out from first oil path 61.
FIGS. 8 and 9 are side and plan sectional views of the conventional electromagnetic pump as shown in FIG. 7.
As shown in detail in FIG. 8, actuating section 31 includes a hollow first cylinder 36. First cylinder 36 has a bobbin 55, a support plate 55a disposed beneath bobbin 55 and in close contact therewith, and a hollow second cylinder 37 fitted in a hole formed at a lower part thereof. Second cylinder 37 has a smaller diameter than that of first cylinder 36.
Bobbin 55 has a solenoid 54 wound on an outer surface thereof. A cap 55b enclosing bobbin 55 and solenoid 54 is disposed on support plate 55a.
First cylinder 36 further has a magnetic core 56 secured in bobbin 55, and a stopper 45 and a plunger assembly 51 movably disposed above and under magnetic core 56, respectively.
Plunger assembly 51 includes a plunger 52 and a piston 53 formed integrally with plunger 52 and extended downward thereof. One end of piston 53 is inserted in second cylinder 37 so as to move up and down therein. A first space and a second space 71 and 72 isolated from each other by piston 53 are formed under and above second cylinder 37, respectively. A first spring 57 is disposed between magnetic core 56 and plunger 52, and a second spring 58 is disposed between plunger 52 and the bottom of first cylinder 36. Also, a third spring 59 is disposed between magnetic core 56 and stopper 45.
A stopper seat 46 is disposed above stopper 45. Stopper 45 and stopper seat 46 constitute exhaust valve 44 as mentioned above. When stopper 45 is at its uppermost position, it engages with stopper seat 46 so as to close exhaust nozzle 48, while exhaust nozzle 48 is open when stopper 45 is moved downward from the uppermost position.
Referring again to FIG. 7, first space 71 formed under piston 53 is interconnected to a third oil path 63 branched out from second oil path 62, and exhaust check valve 34 is interconnected through fourth oil path 64 with second space 72 formed above piston 53. In addition, both an air bleeder valve 38 for exhausting air contained in pressurized oil and a buffer 39 for reducing fluctuation of exhaust of pressurized oil are branched out from fourth oil path 64. Second space 72 formed above piston 53 is interconnected with exhaust valve 44 through fifth oil path 65.
Referring to FIG. 9, relief valve 42 is supported by a fourth spring 43 and biasing force of fourth spring 43 can be preset and adjusted by means of an adjuster 47.
In the conventional electromagnetic pump having the above described construction, oil is pumped as follows.
First, when electric power is applied to solenoid 54, magnetic core 56 is magnetized so that plunger assembly 51 is elevated toward magnetic core 56. At this moment, the volume of first space 71 is expanded so that the pressure in second oil path 62 connected thereto is decreased. Then, suction check valve 32 is open and exhaust check valve 34 is closed, while oil is supplied to second oil path 62 from oil tank 12 through suction nozzle 22, first oil path 61, suction filter 24, and suction check valve 32. At the same time, stopper 45 is lowered toward magnetic core 56 so that exhaust valve 44 is open. To ensure the alternating of both stopper 45 and plunger assembly 51 by magnetic force, bobbin 55 is made from non-magnetic material and both support plate 55a and cap 55b are made from magnetic material.
Meanwhile, when electric power having been applied to solenoid 54 is cut-off, plunger assembly 51 moves downward by means of biasing force of first spring 57. In this case, second spring 58 keeps plunger assembly 51 from being excessively pushed downward in first cylinder 36, so that plunger assembly 51 can be maintained in the range of electromagnetic force of magnetic core 56.
As plunger assembly 51 moves downward, the volume of first space 71 is reduced so that the pressure in second oil path 62 interconnected thereto is increased. Accordingly, suction check valve 32 is closed and exhaust check valve 34 is open, while the oil pressurized in first space 71 is flowed through exhaust check valve 34 and fourth oil path 64 into second space 72. Then, the pressurized oil is flowed from second space 72 through fifth oil path 65 into exhaust valve 44. Air contained in pressurized oil can be exhausted through air bleeder valve 38 while passing through fourth oil path 64. On the other hand, stopper 45 is moved up again and engaged with stopper seat 46 so that exhaust valve 44 is closed again by means of the biasing force of third spring 59.
When exhaust valve 44 is re-open by applying an electric power to solenoid 54, oil having passed through fifth oil path 65 is exhausted through exhaust nozzle 148 to the exterior of the electromagnetic pump, i.e., to the burner.
The above-described process is periodically repeated whenever such applying and cutting off of an electric power alternates. The exhaust pressure of oil is increased according to this periodical repetition. When the exhaust pressure having been increased exceeds a preset biasing force of fourth spring 43 for supporting relief valve 42, relief valve 42 is pushed backward while compressing fourth spring 43. At this moment, sixth and seventh oil paths 66 and 67 are interconnected to each other so that some of the pressurized oil is returned to first oil path 61 through sixth and seventh oil paths 66 and 67, and thereby the exhaust pressure in exhaust valve 44 decreases.
When the exhaust pressure goes down below the biasing force of fourth spring 43, relief valve 42 moves forward again and is returned to the initial position so that sixth and seventh oil paths 66 and 67 are blocked off again from each other, and thereby the exhaust pressure is increased again. In this way, exhaust pressure of the electromagnetic pump is equilibrated at a pressure which can be predetermined by setting up biasing force of fourth spring 43 supporting relief valve 42. By means of adjuster 47, the predetermined pressure can be adjusted.
However, the conventional electromagnetic pump having the above construction has disadvantages as follows.
First, the exhaust of oil is highly pulsative since the pressurized oil is exhausted through exhaust valve 44 which is intermittently open and closed according to the operation of solenoid 54. For this reason, a separate element for reducing pulsation of exhaust oil such as buffer 39 is required.
Further, since alternating current over 60 Hz is generally used as an electric source, stopper 45 should move up and down by a very high speed over 60 times per second so that impact noise between stopper 45 and magnetic core 56 can be generated.
Furthermore, the biasing force of third spring 59 supporting stopper 45 is set irrespective of the pressure of the exhausted oil. For this reason, even after the operation of exhaust valve 44 has been finished, exhaust valve 44 may not be closed completely so that oil of low pressure may leak therethrough to the burner. The oil having low pressure leaked to the burner is not sufficiently vaporized, so it is not completely burned and thereby makes a bad smell after the running of burner has been finished. That is, incomplete combustion happens in the burner after the running of the burner has been finished, which is so-called "a fire-extinction delay" phenomenon.
In addition, since both exhaust valve 44 and exhaust nozzle 48 are disposed in an upper portion of first cylinder 36, air contained in the pressurized oil is concentrated in exhaust valve 44 due to the difference of viscosity between the pressurized oil and air. The concentrated air, unlike oil, can not dampen the operation of stopper 45 so that the impact noise by stopper 45 is further increased.
Moreover, the larger a gap between stopper 45 and an upper wall 36a of first cylinder 36 is, the more the oil leaks therethrough, while the smaller the gap is, the louder the operating noise would be. Accordingly, it is impossible to solve the problems of noise and leakage simultaneously.
Further, an excessive pressure of the exhausted oil over a predetermined value is wasted in the conventional electromagnetic pump. That is, when the exhaust pressure exceeds a predetermined value, a part of the exhausted oil is returned through seventh oil path 67 to first oil path 61 and is recirculated in the electromagnetic pump so as to control the exhaust pressure. Accordingly, there is waste of energy for recirculating such redundant oil.
Furthermore, the magnetic flux or the magnetic force is transferred from solenoid 54 to magnetic core 56 through magnetic support plate 55a and magnetic cap 55b, and thereby it may be weakened due to upper wall 36a of first cylinder 36 which is made of non-magnetic material so as to act as a magnetic void. This weakened magnetic force may also result in waste of energy.